The Rise of the Bobcat T320
The Bobcat T320 compact track loader was introduced in the early 2000s as part of Bobcat’s push into high-performance tracked machines. Designed for demanding applications like grading, demolition, and forestry, the T320 featured a powerful 92-horsepower turbocharged diesel engine and a rated operating capacity of 3,200 pounds. Its robust hydraulic system and vertical lift path made it a favorite among contractors needing reach and lifting power. Bobcat, founded in 1947 and headquartered in North Dakota, has sold millions of loaders globally, with the T-series representing a significant leap in track loader evolution.
Understanding Lift Cylinder Bleed Off
Lift cylinder bleed off refers to the gradual lowering of the loader arms or bucket when the machine is idle or under light load. In hydraulic systems, this typically results from internal leakage past the piston seals or faulty control valves. After a cylinder rebuild, the expectation is that the issue should resolve. However, persistent bleed off suggests deeper hydraulic inefficiencies.
In the case of the T320, even after both lift cylinders were rebuilt and external leaks eliminated, the bucket continued to drop slowly. This points to internal bypassing, where hydraulic fluid leaks past the piston seal inside the cylinder, or valve block leakage, where the control valve fails to hold pressure.
Bobtach System and Pedal-Dependent Closure
The Bobtach system, Bobcat’s proprietary quick-attach mechanism, allows operators to switch attachments rapidly. It’s hydraulically actuated and controlled via foot pedals. A common issue arises when the Bobtach fails to close unless the left pedal is depressed, and even then, it closes slowly. This behavior suggests low hydraulic pressure, restricted flow, or valve block malfunction.
Despite replacing the Bobtach valve block and actuator just six months prior, the issue resurfaced. This recurrence may be due to:
To isolate the problem, technicians should perform the following:
Preventive Measures and Recommendations
To prevent recurrence and extend system life:
One operator in Kentucky rebuilt his cylinders twice before discovering that the replacement seals were aftermarket and slightly undersized. After switching to factory seals, the bleed off stopped. Another contractor found that a loose ground wire behind the operator seat caused intermittent valve actuation, affecting both the Bobtach and lift functions.
Conclusion
The T320’s hydraulic system is powerful but sensitive to component integrity and fluid quality. Persistent lift cylinder bleed off after rebuilds often indicates internal bypassing or valve block failure. Similarly, Bobtach issues tied to pedal actuation suggest pressure or electrical faults. With proper diagnostics, OEM parts, and preventive maintenance, these problems can be resolved, restoring the machine’s full lifting and attachment capabilities. The T320 remains a reliable workhorse, but like all high-performance equipment, it demands attention to detail and proactive care.
The Bobcat T320 compact track loader was introduced in the early 2000s as part of Bobcat’s push into high-performance tracked machines. Designed for demanding applications like grading, demolition, and forestry, the T320 featured a powerful 92-horsepower turbocharged diesel engine and a rated operating capacity of 3,200 pounds. Its robust hydraulic system and vertical lift path made it a favorite among contractors needing reach and lifting power. Bobcat, founded in 1947 and headquartered in North Dakota, has sold millions of loaders globally, with the T-series representing a significant leap in track loader evolution.
Understanding Lift Cylinder Bleed Off
Lift cylinder bleed off refers to the gradual lowering of the loader arms or bucket when the machine is idle or under light load. In hydraulic systems, this typically results from internal leakage past the piston seals or faulty control valves. After a cylinder rebuild, the expectation is that the issue should resolve. However, persistent bleed off suggests deeper hydraulic inefficiencies.
In the case of the T320, even after both lift cylinders were rebuilt and external leaks eliminated, the bucket continued to drop slowly. This points to internal bypassing, where hydraulic fluid leaks past the piston seal inside the cylinder, or valve block leakage, where the control valve fails to hold pressure.
Bobtach System and Pedal-Dependent Closure
The Bobtach system, Bobcat’s proprietary quick-attach mechanism, allows operators to switch attachments rapidly. It’s hydraulically actuated and controlled via foot pedals. A common issue arises when the Bobtach fails to close unless the left pedal is depressed, and even then, it closes slowly. This behavior suggests low hydraulic pressure, restricted flow, or valve block malfunction.
Despite replacing the Bobtach valve block and actuator just six months prior, the issue resurfaced. This recurrence may be due to:
- Contaminated hydraulic fluid damaging seals or clogging orifices.
- Faulty solenoids in the valve block not fully energizing.
- Electrical grounding issues affecting valve response.
To isolate the problem, technicians should perform the following:
- Pressure test the lift circuit at the cylinder ports. Compare static holding pressure with manufacturer specs.
- Inspect the control valve block for wear, debris, or sticking spools.
- Check the hydraulic fluid for contamination, aeration, or viscosity breakdown.
- Verify pedal linkage and sensor feedback to ensure proper signal transmission.
Preventive Measures and Recommendations
To prevent recurrence and extend system life:
- Flush the hydraulic system every 1,000 hours or annually, whichever comes first.
- Use OEM-grade seals and components during rebuilds to ensure compatibility.
- Install a magnetic inline filter to trap metallic debris.
- Monitor pedal response and recalibrate sensors during routine service.
One operator in Kentucky rebuilt his cylinders twice before discovering that the replacement seals were aftermarket and slightly undersized. After switching to factory seals, the bleed off stopped. Another contractor found that a loose ground wire behind the operator seat caused intermittent valve actuation, affecting both the Bobtach and lift functions.
Conclusion
The T320’s hydraulic system is powerful but sensitive to component integrity and fluid quality. Persistent lift cylinder bleed off after rebuilds often indicates internal bypassing or valve block failure. Similarly, Bobtach issues tied to pedal actuation suggest pressure or electrical faults. With proper diagnostics, OEM parts, and preventive maintenance, these problems can be resolved, restoring the machine’s full lifting and attachment capabilities. The T320 remains a reliable workhorse, but like all high-performance equipment, it demands attention to detail and proactive care.
